Pleistocene Epoch

[Sunsettommy]

Ohio History Central

July 1, 2007

EXCERPT:

About 1.8 million years ago, the warm climate of the Cenozoic Era cooled sufficiently for large continental glaciers to begin to accumulate in far northern latitudes. As the ice built to a great thickness, it began to slowly flow outward and into the northern United States, including about two-thirds of Ohio. Thus began the Pleistocene Ice Age, which profoundly changed Ohio’s landscape to the benefit of our society and left the first record of geologic events in Ohio since more than 290 million years ago.

Ice ages are complex events that are poorly understood and may be initiated by variations in the output of the sun, perturbations in the earth’s orbit and revolution, continental configurations, and ocean circulation. A long ice age has many intervals of glacial advance and retreat with warmer interglaciations between the glacial advances. The classic interpretation of these advances and retreats in the Midwest is four major glacial advances named after states in which their deposits are prominent. They are, from oldest to youngest: Nebraskan, Kansan, Illinoian, and Wisconsinan. Geologists now recognize that the Pleistocene was more complex than implied by this four-fold division. In Ohio, the earlier glaciations, before the Illinoian, are lumped as “pre-Illinoian.” These deposits are known in Ohio from deeply weathered sediments exposed in a small area in Hamilton County, near Cincinnati.

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